1. Field of the Invention
This invention pertains to devices made of thermoplastic elastomeric films such as condoms, and in particular, relates to a method for providing convolutions on said films, and to condoms and other devices made of films having portions containing convolutions.
2. Description of the Related Art
Recent significant increases in the incidence and spread of sexually transmitted diseases (STD's), as well as the desire for methods of family planning not requiring use of birth control pills, have resulted in increased use of condoms to reduce transmission both of STD bacteria and of viable sperm.
Condoms are generally elongated tubular sheaths made of a thin flexible material, such as latex resins (natural rubber). Generally, latex resins are used to coat cylindrical molds with a thin layer by a dipping process. The thickness of the rubber coating may vary depending on the viscosity of the latex and the speed of extracting the mold from the latex.
Although, obtaining uniformity is a problem with making condoms of latex, one advantage of natural rubber condoms is that lower initial force is required to stretch a film of natural rubber than to stretch films of many synthetic elastomeric films.
Condoms of a variety of synthetic materials have been developed to improve the strength and reliability characteristics of condoms. It is desirable to use thermoplastic elastomeric films instead of latex or less elastic thermoplastic films because of unique permeability, formability, environmental resistance, mechanical and economy considerations. For example, condoms may be formed of thermoplastic polyurethane materials, such as polyether-or polyester-based urethane elastomers (U.S. Pat. No. 4,576,156 of Dyke), and a polyurethane prepolymer which is the reaction product of a polyisocyanate compound with at least one long chain polyol (Eur. patent application 0 147 072 of Taller et al.). The disclosure of these patents is incorporated herein by reference.
Condoms amenable to construction from thermoplastic elastomeric materials are disclosed in co-pending application, Ser. No. 07/271,884 filed Nov. 15, 1988, the disclosure of which application is hereby incorporated herein.
Specific examples of non-rubber materials used for condoms include, polyurethane materials, for example, the polyesterbased and polyether-based polyurethane materials commercially available from Mobay Corporation such as TEXIN.sup..TM.,(Plastics and Rubber Division, Pittsburgh, Pa.); the thermoplastic polyurethane elastomers which are commercially available from BASF Corporation (Parsippany, N.J.) under the trademark ELASTOLLAN.sup..TM. (PLATILON.sup..TM.); polyester elastomers, such as the block copolymers of polybutylene terephthalate and long chain polyether glycols, which are commercially available from E. I. DuPont de Nemours and Co., Inc. (Polymer Products Dept., Engineering Polymers Div., Wilmington, Del.) under the trademark HYTREL.sup..TM. ; other polyester polyurethane elastomers such as PELLETHANE.sup..TM. (Bertek, St. Albans, Vt.); polyether blockamides, such as those commercially available from Atochem, Inc. (Glenrock, N.J.) under the trademark PEBAX.sup..TM. ; multiblock rubberbased copolymers, such as are commercially available from Shell Chemical Co. (Houston, Tex.) under the trademark KRATON.sup..TM. ; ethylene-octene copolymers such as those commercially available from the Dow Chemical Co. (Midland, Mich.) under the trademark ATTANE.sup..TM., as well as any other suitable homopolymers and copolymers, and mixtures, alloys, and composites thereof.
The synthetic materials used for condoms generally have less elasticity (more resistance to stretch) and show more viscoelastic creep than natural rubber. The higher elastic modulus of thermoplastic elastomers causes them to be less desirable for condoms than latex because of a greater stiffness. The lower creep resistance of thermoplastic elastomers causes a problem because they lose their shape when they are rolled for packaging.
The elastic moduli of many thermoplastic elastomers that might be or are being used for condoms are high relative to latex and do not allow for easy donning of the condoms and a secure fit over a wide range of penis circumferences.
Resin suppliers and manufacturers have attempted to remedy this situation by altering the chemical composition of the synthetic polymers and by adding plasticizers. Softening with plasticizer complicates the governmental approval process for intimate human use and causes undesirable changes in some mechanical properties such as tear resistance.
Thermoplastic films as produced by casting, extrusion or by extrusion blowing are generally in the form of flat planar films rolled onto reels. Many of the applications of the films in the form of bags, covers, garments, pouches and the like require that the film be wrinkled or folded to make it conform to a surface that cannot be generated from a planar film. An alternative is to take a planar film that has been highly folded throughout and to make it conform to irregular shapes by stretching. When the pattern of convolutions in the film has a curvature to film thickness ratio that allows the film to be flattened without exceeding its elastic limit, it will behave as an elastic membrane when it is stretched and contracted reversibly.
A patent application is in preparation entitled "TEXTURED THERMOPLASTIC ELASTOMERIC FILM AND ARTICLES COMPRISING SAME," which discloses a method of improving film elasticity of thermoplastic elastomeric films by heat embossing (texturizing) the film, and items made from such film. This texture is a "microtexture" and provides a limited stretching range before the embossing is exhausted and causes thinning of the film.
One way of obtaining differential effects on various portions of metallic materials after exposure to certain treatment parameters utilizes bimetallic strips. Such strips increase in curvature with temperature because the two components have different thermal coefficients of expansion. Such differential expansion is useful to provide a controlled change in form of a metallic substance at a given treatment time.
It is therefore an object of the invention to provide films having areas of different coefficients of solvent-mediated expansion, for example, of hydroscopic expansion.
It is also an object of this invention to provide a method for treating elastomeric film so that large changes may be produced in the area covered by the film without changing the film thickness or surface area of the film.
It is a further object of the invention to provide a means for treating a portion of an elastomeric film so that portion is self-puckering into convolutions when treated with an appropriate agent.
It is a further object of the invention to provide items made from elastomeric film, and which have all or a portion of the item treated to self-pucker and/or form convolutions when treated with an agent.
It is a further object of the invention to provide items which have a plurality of self-puckering areas.
It is a further object of the invention to provide thermoplastic films capable of conforming reversibly to irregular shapes.
Other objects and advantages of the invention will be more fully apparent from the following disclosure and appended claims.